Motor vehicle gearbox

ABSTRACT

Motor vehicle gearbox with two concentrically mounted input shafts, each driving an individual layshaft, having gears in engagement with gears on an output shaft. One layshaft has a central synchronization device, via which the layshaft which is driveably coupled to the momentarily non-driven input shaft, can be accelerated up to a rotational speed chosen by the selected gear speed. The central synchronization device has a friction clutch and two synchronization gears of different diameter, the gear of smaller diameter being widened relative to the other and being lockable to the shaft by an engagement sleeve, so that drive torque can be transmitted via the synchronization gear. The second layshaft is releasable by an engagement device, whereby torque can be transmitted from one layshaft to the other and to the output shaft.

FIELD OF THE INVENTION

The present invention relates to a motor vehicle gearbox, comprising atleast two concentrically arranged alternately driveable first and secondinput shafts, first and second layshafts, primary gears carried by thefirst input shaft and the first layshaft, said primary gears engagingeach other for transmitting torque from the first input shaft to thefirst layshaft, primary gears carried by the second input shaft and thesecond layshaft, said primary gears engaging each other for transmittingtorque from the second input shaft to the second layshaft, an outputshaft, gears carried by the layshafts and the output shaft, said gearsengaged in each other in pairs for transmitting torque from eitherlayshaft to the output shaft and of which at least one gear in each pairis a releasable idle gear, and synchronizing means comprising firstly apair of synchronizing gears of different diameters rotatably mounted onone of the layshafts, said gears being in driving engagement with gearrings on one input shaft, and secondly friction means, by means of whicha driving connection between one synchronizing gear and the shaft can beestablished to adapt the rotational speed of the layshaft which isdriveably coupled to the momentarily undriven input shaft, to arotational speed determined by the selected gear speed, at least thesynchronizing gear of smaller diameter being coordinated with engagingmeans which permits transmission of higher torque to its layshaft thanwhat is required for said rotational speed adaption.

BACKGROUND OF THE INVENTION

A gearbox of the above stated type is previously known from SE-A-507366. It is based on a so-called “power-shift” gearbox with atwo-position central synchronization, whereby six synchronizingfunctions are obtained in a seven-speed gearbox with two synchronizinggears and a synchronizing clutch on one of the layshafts. It is furtherdeveloped in that one of the synchronizing gears is made so that it canalso be used for torque transmission to provide an additional gearspeed, namely an overdrive. Practically, this can be achieved bywidening one of the normally quite narrow synchronization gears andproviding it with engaging means which provides a shape engagementinstead of a friction engagement.

OBJECT OF THE INVENTION

The purpose of the present invention is, in a gearbox of the typedescribed by way of introduction, to increase the number of gear ratioswith the smallest possible economic investment and design work.

SUMMARY OF THE INVENTION

This is achieved according to the invention by virtue of the fact thatthat the primary gear of the second layshaft is coordinated withengaging means, whereby the primary gear is releasable from and lockableto its shaft, and that the primary gear is releasable from its shaft atthe same time as the synchronizing gear of smaller diameter is lockableby means of its engagement means to its shaft to permit torquetransmission from the second input shaft via said synchronization gearand inter-engaging gears on the first and second layshafts to the outputshaft.

Merely by arranging the primary gear of the second layshaft to bereleasable, which is known per se in other contexts, and coordinatingthis release with the engagement of the other synchronization gear, i.e.the overdrive gear, a second reverse gear is obtained with a lower gearratio than the existing reverse gear. To do such design work, only oneadditional engaging means is required to provide the gearbox the gearboxshown in SE-A-507 366 with an additional gear speed.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in more detail with reference to anexample shown in the accompanying drawing, where the FIGURE shows alongitudinal section through a gearbox with seven regular gears plusoverdrive and reverse gear.

DETAILED DESCRIPTION OF THE DRAWING

l in the Figures designates an engine fly wheel, which via a multi-diskwet disk clutch, generally designated 2, drives a gearbox 3 according tothe invention. The clutch 2 is a double clutch of a type known per seand therefore it does not need to be described in more detail here. Theleft hand clutch unit 4 seen in the FIGURE is coupled via a sleeveelement 5 to a first input shaft 6 in the gearbox, while the right handclutch unit 7 is coupled via a sleeve element 8 to a second input shaft9 in the form of a hollow shaft mounted concentrically with the firstshaft 6. The two clutch units can be alternately engaged and disengagedto alternately drive the input shafts 6 and 9. The wet disk clutch showncan be replaced by a double dry disk clutch.

The first input shaft 6 is provided with a gear ring 10, in engagementwith a gear 111 which is solidly mounted on a first layshaft 12. Thesecond input shaft 9 is made with a gear ring 13 which is in engagementwith a gear 14 which is mounted on a second layshaft 15. The gear ring13 is larger than the gear ring 10, which means that the second layshaft15 will rotate more rapidly than the first layshaft 12 at the same inputrpm for the respective input shaft.

The layshafts 12 and 15 respectively each support a pair of freelyrotatably mounted gears 16, 17 and 18, 19 respectively, of which thegears 16, 18 are both in engagement with a gear 21 fixedly mounted onthe output shaft 20, and the gears 17, 19 are in engagement with a gear22 which is rotatably mounted on the output shaft and can be locked tothe shaft with the aid of an engaging sleeve 27. The shafts are arrangedin a V shape in order to make it possible, with the aid of an extra gear23 on the layshaft 15, said gear engaging the gear 11 on the layshaft12, to reverse the rotational direction of one of the layshafts forproviding a reverse gear. It is also possible to reverse the rotationaldirection of the respective layshaft by means of a gear mounted on aseparate shaft in the housing, said gear engaging the gear rings 10 and23. This provides a freer selection of V shape and gear ratios and alsopermits the shafts to be placed in the same plane. The gears 16, 17, 18,19 and 23 are lockable to their shafts with the aid of axiallydisplaceable engaging sleeves 24, 25 and 26. A gear 40 freely rotatablymounted on the output shaft 20 engages the gear ring 41 integral withthe layshaft 15 and is lockable to the shaft 20 by means of an engagingsleeve 42. By cutting the gear ring 41 directly in the layshaft 15 andarranging the gear 40 lockable to the output shaft, the need for needlebearings on the layshaft is eliminated and the gear can be made with avery small diameter, which in turn provides a higher gear ratio from thelayshaft to the output shaft. With the aid of the engaging sleeve 27,the input shaft 6 and the output shaft 20 can be locked together fordirect drive. All of these engaging sleeves are without individual,conventional synchronizing devices.

The first layshaft 12 is instead co-ordinated with a centralsynchronizing device generally designated 30. It comprises a pair ofgears 32, 33 freely rotatably mounted on an extension 31 of the layshaft12 with a clutch disk 34 therebetween. The clutch disk 34 is axiallydisplaceable but non rotatably mounted relative to the shaft 12 by meansof splines. The clutch disk is joined to operating means, not shown inmore detail here, for controlling the shifting. The synchronizing gears32, 33 have on their sides facing the disk 34 frictional surfaces 37,38. The left hand gear 32 engages a gear ring 39 on the second inputshaft 9. The gear ring 39 has a smaller diameter than the gear ring 10on the first input shaft. The right hand synchronizing gear 33 engagesthe gear ring 13 on the second input shaft and here there is preferablya difference of one or two gear teeth between the synchronizing gear 33and the driven gear 14 on the second layshaft.

For more detailed description of the synchronizing sequence reference ismade to SE-A-507 366.

In order to be able to utilize the synchronizing gear 33 for torquetransmission it has been widened relative to the gear 32 and coordinatedwith an engagement device 60 which provides a shape-bound engagement.The engagement device 60 comprises a hub 61 solidly joined to thelayshaft 12. The hub 61 has external splines 62 which engagecorresponding internal splines on the engagement sleeve 63. The gear 33is provided with a ring of splines 64.

When torque is to be transmitted via the synchronization gear 33 thegear is locked to the shaft by axial displacement of the engagementsleeve 63, so that its splines engage with the splines 64 of the gear33. The torque is now transmitted as indicated by the dash-dot OD linein the FIGURE, thereby providing an additional gear speed, an overdrive,which has a higher rpm on the output shaft 20 than on the input shaft 6.

According to the invention the primary gear 14 of the second layshaft isfreely rotatably mounted on the shaft and is coordinated with anengagement device 55 which comprises a hub 56, non-rotatably joined tothe layshaft 15. The hub has external splines 57 which engagecorresponding internal splines on an engagement sleeve 58. The gear 14is made with a ring of splines 59.

With the gear 33 locked on the layshaft 12 and gear 14 released from thelayshaft 15, torque can be transmitted from the layshaft 12 to thelayshaft 15 and from there to the output shaft 20, as marked with theline R2 in the FIGURE, thus providing a faster reverse gear, i.e. areverse gear with a lower gear ratio than the ordinary reverse gear. Thetorque path for the ordinary reverse gear is marked with the line R1 inthe FIGURE.

What is claimed is:
 1. A motor vehicle gearbox, comprising at least twoconcentrically arranged alternately driveable first and second inputshafts (6,9), first and second layshafts (12,15), first and secondprimary gears carried by the first input shaft (6) and the firstlayshaft (12) respectively, said first and second primary gears (10,11)engaging each other for transmitting torque from the first input shaft(6) to the first layshaft (12), third and fourth primary gears (13,14)carried by the second input shaft (9) and the second layshaft (15)respectively, said third and fourth primary gears engaging each otherfor transmitting torque from the second input shaft (9) to the secondlayshaft (15), an output shaft (20), gears (16,17,18,19,21,22) carriedby the layshafts and the output shaft, said gears being engaged in eachother in pairs for transmitting torque from either layshaft to theoutput shaft and of which at least one gear in each pair is a releasableidler gear, and synchronizing means (30) comprising firstly a pair ofsynchronizing gears (32, 33) of different diameters rotatably mounted onsaid first layshaft, said synchronizing gears being in drivingengagement with said third primary gear (13) and a gear ring (39) onsaid second input shaft (9), and secondly friction means (34), by meansof which a driving connection between one of said synchronizing gears(32, 33) and the first layshaft (12) can be established to adapt therotational speed of the first layshaft which is driveably coupled to amomentarily undriven input shaft, to a rotational speed determined by aselected gear speed, at least the synchronizing gear (33) of smallerdiameter being coordinated with first engaging means (60) which permitstransmission of higher torque to said first layshaft than what isrequired for a rotational speed adaption, characterized in that saidfourth primary gear (14) of the second layshaft (15) is coordinated withsecond engaging means (55), whereby said fourth primary gear (14) isreleasable from and lockable to it said second layshaft (15), and thatsaid fourth primary gear is releasable from said second layshaft (15) atthe same time as the synchronizing gear (33) of smaller diameter islockable, by means of said first engaging means (60) to said firstlayshaft (12) to permit torque transmission from the second input shaft(9) via one of said synchronization gears (33) and said first and secondprimary gears (11,12) on the first and second layshafts (12,15) to theoutput shaft (20).
 2. The gearbox according to claim 1, characterized inthat the synchronization gear (33) of smaller diameter is coordinatedwith said first engaging means (60), which permits transmission ofhigher torques to said first layshaft (12) than the friction means (34).3. The gearbox according to claim 1, characterized in that thesynchronization gear (33) of smaller diameter engages said third primarygear (13) arranged on said second input shaft (9) and that the gearratio between these latter gears is lower than the gear ratio betweenthe first primary gear (10) of the first input shaft (6) and the secondprimary gear (11) in engagement therewith, on the first layshaft (12).4. The gearbox according to claim 1, characterized in that thesynchronizing gear (33) of smaller diameter has a gear ring of largeraxial dimension than the gear ring of the second synchronization gear(32).
 5. The gearbox according to claim 1, characterized in that thefirst engaging means (60) comprise an engaging hub (61) non-rotatablyjoined to the first layshaft (12), said hub, non-rotatably but axialllydisplaceably carries an engagement sleeve (63) with internal engagingteeth (62), which upon displacement of the engagement sleeve in onedirection are insertable into engagement with corresponding engagementteeth (64) on the synchronization gear (33) for locking it to the firstlayshaft (12).
 6. The gearbox according to claim 2, characterized inthat the synchronization gear (33) of smaller diameter engages saidthird primary gear (13) arranged on said second input shaft (9) and thatthe gear ratio between these latter gears is lower than the gear ratiobetween the first primary gear (10) of the first input shaft (6) and thesecond primary gear (11) in engagement therewith, on the first layshaft(12).